The Edwards SAPIEN XT transcatheter heart valve (THV) system will be studied in patients deemed inoperable or intermediate risk. A subset of inoperable patients will be randomized to receive transcatheter aortic valve replacement (TAVR) with either the SAPIEN XT THV or the SAPIEN THV. The SAPIEN XT will be studied in intermediate risk patients randomized to receive TAVR with the SAPIEN XT or surgical AVR.